Strip accumulators heretofore have stored a length of strip material in an expanding and contracting spiral coil having a fixed number of turns with the strip material being fed to the inside of the spiral coil and withdrawn from the outside, or vice versa. Typically, the maximum diameter of the outermost turn of the spiral coil is determined by an outer containment ring or circular array of outer containment rollers, whereas the inner diameter of the innermost turn of the spiral coil is determined by an inner containment ring or circular array of inner containment rollers. Accordingly, the difference between the length of coil when fully expanded into engagement with the outer containment ring or rollers and when fully contracted against the inner containment ring or rollers determines the maximum reserve storage capacity of the accumulator for any given gauge and number of turns of the strip material.
It of course will be understood that the radial dimension of the space occupied by such given number of turns in the spiral coil when the turns are closely packed must be less than the difference between the maximum and minimum permissible radii of the spiral coil defined by the outer and inner containment rings or rollers.
Such inner and outer containment rings or rollers typically are mounted in the accumulator at respective fixed diameters. However, it is known to mount inner containment rollers for slight radial movement so that they can be radially retracted away from the contacted spiral coil just prior to resumption of strip feed-in to the inside of the spiral coil following attachment of a new coil of strip material to the end of the spent coil.
In one known type of strip accumulator disclosed in United Kingdom Patent Specification No. 1,386,250, an annular ring or array of long, thin, cylindrical rollers support a single spiral coil of strip material with the axis thereof oriented vertically, and such rollers are synchronously driven by individual variable speed electric motors to rotate the spiral coil of strip material supported thereon to facilitate feeding and withdrawal of the strip material from the spiral coil. The rollers extend radially, or may be slightly skewed, and slope downwardly and outwardly to urge the turns of the spiral coil stored thereon outwardly as the rollers rotate.
It also is known to guide the incoming strip material by a support cage mounted above the individually driven rollers and feed the strip material to the inside of the spiral coil and withdraw the strip material from the outside, or vice versa. Such support cage includes a driven pair of feed-in or pinch rollers and one or more pairs of fixedly mounted guide idler rollers which define a desired helical path of the strip material from the pinch rollers to the individually driven rollers supporting the spiral coil.
Although such an accumulator will operate satisfactorily, it is relatively expensive to manufacture and is subject to misoperation. In particular, the individually driven rollers and drives therefor are expensive, and sophisticated controls are requried to achieve proper synchronization of the rollers. Moreover, the turns of the spiral coil of strip material are not positively controlled, and undesirable interface friction exists between adjacent closely packed turns of the spiral coil, which may also cause the surfaces of the strip material to become marred, blemished or otherwise damaged as a result of the rubbing that occurs between adjacent turns of the spiral coil.